Additives in gypsum slurries and adjusting their proportions

ABSTRACT

A gypsum slurry is provided that includes calcium sulfate hemihydrate; water; a dispersant component comprising at least one of the following a comb-branched polymer with polyether side chains, naphthalene sulfonate-formaldehyde condensate or melamine sulfonate-formaldehyde condensate; a foaming agent; and a polycondensation component with three polycondensation repeating units. Also provided is a method for making a gypsum slurry with a foaming agent in which the ratio between the dispersant component and the polycondensation component is adjusted to control for the size of foam bubbles in the gypsum slurry. Gypsum products made from the gypsum slurry are provided and methods for making the products are provided as well.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/870,381, filed Aug. 27, 2010, which claimspriority under 35 USC 119(e) from U.S. Ser. No. 61/239,259 filed Sep. 2,2009 and entitled, “Additives in Gypsum Panels and Adjusting TheirProportions,” herein incorporated by reference. This application isrelated to U.S. Ser. No. 12/552,338, filed Sep. 2, 2009 and entitled“Formulation and Its Use,” herein incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to gypsum products. More specifically, it relatesto a gypsum-based panel that requires less time or less energy fordrying than conventional products.

Gypsum-based panels are commonly used in construction. Wallboard made ofgypsum is fire retardant and can be used in the construction of walls ofalmost any shape. It is used primarily as an interior wall or exteriorwall or ceiling product. Gypsum has sound-deadening properties. It isrelatively easily patched or replaced if it becomes damaged. There are avariety of decorative finishes that can be applied to the wallboard,including paint and wallpaper. Even with all of these advantages, it isstill a relatively inexpensive building material.

One reason for the low cost of wallboard panels is that they aremanufactured by a process that is fast and efficient. Calcium sulfatehemihydrate hydrates in the presence of water to form a matrix ofinterlocking calcium sulfate dihydrate crystals, causing it to set andto become firm. A slurry that includes the calcium sulfate hemihydrateand water is prepared in a mixer. When a homogeneous mixture isobtained, the slurry is continuously deposited on a moving surface thatoptionally includes a facing material. A second facing material isoptionally applied thereover before the slurry is smoothed to a constantthickness and shaped into a continuous ribbon. The continuous ribbonthus formed is conveyed on a belt until the calcined gypsum is set, andthe ribbon is thereafter cut to form panels of desired length, whichpanels are conveyed through a drying kiln to remove excess moisture.Since each of these steps takes only minutes, small changes in any ofthe process steps can lead to gross inefficiencies in the manufacturingprocess.

The amount of water added to form the slurry is in excess of that neededto complete the hydration reaction. Excess water gives the slurrysufficient fluidity to flow out of the mixer and onto the facingmaterial to be shaped to an appropriate width and thickness. As theproduct starts to set, the water pools in the interstices betweendihydrate crystals. The hydration reaction continues building thecrystal matrix in and around the pools of water, using some of thepooled water to continue the reaction. When the hydration reactions arecomplete, the unused water occupying the pools leaves the matrix byevaporation. Interstitial voids are left in the gypsum matrix when allwater has evaporated. The interstitial voids are larger and morenumerous where large amounts of excess water are used.

While the product is wet, it is very heavy to move and relativelyfragile. The excess water is removed from the board by evaporation. Ifthe excess water were allowed to evaporate at room temperature, it wouldtake a great deal of space to stack and store wallboard while it wasallowed to air dry over a relatively lengthy time period or to have aconveyor long enough to provide adequate drying time. Until the board isset and relatively dry, it is somewhat fragile, so it must be protectedfrom being crushed or damaged.

To hasten evaporation, the wallboard panel is usually dried byevaporating the excess water at elevated temperatures, for example, inan oven or kiln. It is relatively expensive to operate the kiln atelevated temperatures, particularly when the cost of fossil fuels rises.A reduction in production costs could be realized by reducing the amountof excess water present in set gypsum boards that is later removed byevaporation.

Dispersants are known for use with gypsum that help fluidize the mixtureof water and calcium sulfate hemihydrate so that less water is needed tomake a flowable slurry.

β-Naphthalene sulfonate formaldehyde (“BNS”) and melamine sulfonateformaldehyde (“MFS”) condensate dispersants are well known, but havelimited efficacy. The preparation and use of BNS is well known state ofthe art and disclosed in EP 0 214 412 A1 and DE-PS 2 007 603, hereinincorporated by reference. The effect and properties of BNS can bemodified by changing the molar ratio between formaldehyde and thenaphthalene component that usually is from about 0.7 up to about 3.5.The ratio between formaldehyde and the sulfonated naphthalene componentpreferably is from about 0.8 to 3.5 to about 1. BNS condensates areadded to the hydraulic binder containing composition in amounts fromabout 0.01 up to about 6.0 wt. %.

Melamine-sulfonate-formaldehyde-condensates are broadly used as flowimproving agents in the processing of hydraulic binder containingcompositions such as dry mortar mixtures, pourable mortars and othercement bonded construction materials and in the production of gypsumpanels. Melamine is used in this connection as representative ofs-triazine. They cause a strong liquefying effect of the constructionchemicals mixture while minimizing undesired side effects occurring inthe processing or in the functional properties of the hardened buildingmaterial. As it is for the BNS technology, there is also broad prior artfor MFS. MFS dispersants are revealed in DE 196 09 614 A1, DE 44 11 797A1, EP 0 059 353 A1 and DE 195 38 821A1.

DE 196 09 614 A1 discloses a water soluble polycondensation productbased on an amino-s-triazine and its use as plasticizer in aqueousbinder containing suspensions based on cement, lime and gypsum. Thesepolycondensates are capable in two condensation steps whereby in apre-condensation step the amino-s-triazine, the formaldehyde componentand the sulfite are condensed at a molar ratio of 1 to 0.5:5.0 to0.1:1.5. Melamine is a preferred representative of amino-s-triazines.Further suitable representatives are amino plast former selected fromthe group urea, thiourea, dicyandiamide or guanidine and guanidinesalts.

According to DE 44 11 797 A1 sulfanilic acid-containing condensationproducts based on amino-s-triazines that show at least two amino groupsare prepared by using formaldehyde. The sulfanilic acid is used inamounts of from 1.0 to 1.6 mol per mol amino-s-triazine and neutralizedin aqueous solution with an alkaline metal hydroxide or in earthalkaline metal hydroxide. In an additional step the formaldehyde isadded in amounts of from 3.0 to 4.0 mol per mol amino-s-triazine at a pHvalue between 5.0 to 7.0 and at temperatures between 50 and 90° C. Thefinal viscosity of the solution is between 10 and 60 cSt at 80° C.

According to EP 0 059 353 A1 highly concentrated and low viscosityaqueous solutions of melamine/aldehyde resins are capable by reactingmelamine and an aldehyde in an alkaline medium in a first step with acomponent selected from the group comprising alkali sulphate, earthalkali sulphate or (earth) alkali sulfonate or other suitable aminocompounds to a pre-condensate. This mixture in an additional processstep is reacted with another amino compound such as amino acids or aminocarbonic acids and finally the resin solution is brought to an alkalinepH value.

DE 195 38 821A1 discloses a condensate based on an amino-s-triazine withat least two amino groups and formaldehyde, and a high content ofsulfonic acid groups and a low content of formate. Such products can beprepared according to this document by reacting the amino-s-triazine,formaldehyde and a sulfite at a molar ratio of 1:3.0:6.0:1.51:2.0 in anaqueous solution and at a temperature between 60 and 90° C. and a pHvalue between 9.0 and 13.0 until the sulfite is no longer present. In anadditional step the condensation process is conducted at a pH valuebetween 3.0 and 6.5 and at temperatures between 60 and 80° C. until thecondensation product at 80° C. shows a viscosity between 5 and 50 mm²/s.Finally, the condensation product is to be brought to a pH value between7.5 and 12.0 or treated thermally by a pH≧10.0 and a temperature between60 and 100° C.

Polycarboxylate dispersants are commonly used with cements and, to alesser degree, with gypsum. The class of compounds represented by theterm “polycarboxylate dispersants” is large, and it is very difficult topredict how individual compounds react in different media. The use of atwo-monomer polycarboxylate dispersant in gypsum products is disclosedin U.S. Pat. No. 7,767,019, herein incorporated by reference.

As has been previously disclosed, many polycarboxylate dispersants havedeleterious effects on gypsum-based products. These dispersants retardsetting of the calcined gypsum. The degree of retardation depends on theexact formulation of the polycarboxylate dispersant. Somepolycarboxylate dispersants also cause a loss in compressive strength offoamed gypsum casts due to stabilization of foam. This leads toformation of smaller voids within the set gypsum. It is difficult topredict how severely a polycarboxylate dispersant will react in a gypsumslurry merely from the chemical formula.

A relatively new class of dispersants has become known for use incements. It is a phosphated polycondensate dispersant. Although thisdispersant is very effective for use in cement, it has lower efficacy ingypsum slurries compared to polycarboxylate dispersants, but it is alsolow in set retardation.

WO 2006/042709 describes polycondensates based on an aromatic orheteroaromatic compound (A) having 5 to 10 C atoms or heteroatoms,having at least one oxyethylene or oxypropylene radical, and an aldehyde(C) selected from the group consisting of formaldehyde, glyoxylic acidand benzaldehyde or mixtures thereof, which result in an improvedplasticizing effect of inorganic binder suspensions compared with theconventionally used polycondensates and maintain this effect over alonger period (“slump retention”). In a particular embodiment, these mayalso be phosphated polycondensates. The phosphated monomers used are,however, relatively expensive since they have to be separately preparedand purified.

Alternatively, there has been developed an economical dispersant, basedon a phosphated polycondensate, for hydraulic binders, which dispersantis particularly suitable as a plasticizer/water-reducing agent forconcrete and can be prepared in a simple manner and at low cost. It isdescribed in provisional application EP 081659155.3, filed in August2008.

Those who install gypsum panels become fatigued by continuously movingand lifting the panels. It is, therefore advantageous to make panelsthat are lightweight for ease in handling. Lightweight panels can bemade by adding foam to the gypsum slurry. A foaming agent, such as soap,can be added to the slurry so that foam is produced by the mixingaction. In some cases, the foaming agent is used to pregenerate a foamthat is added to the slurry after it exits the mixer. The foaming agentis selected to produce a foam that is actively coalescing whilehydration is taking place. A distribution of foam bubble sizes resultsfrom an “active” foam. As the hydration reactions proceed, the gypsummatrix builds up around the foam bubbles, leaving foam voids in thematrix when the set gypsum forms and the foam bubbles break.

It can be difficult to obtain a distribution of foam voids that resultsin an acceptable panel strength. Foam voids that are very small andnumerous have very thin walls of gypsum matrix between them. Poorcompressive strength of the finished panel may result. Formation of verylarge foam voids can produce unevenness in the surface of the panel,making it aesthetically unacceptable. It has been found that when theset gypsum has a distribution of large and small foam voids, the panelcan have both strength and an aesthetically pleasing appearance. Thisfoam void distribution can be achieved by using a combination of soapsthat form stable foam and soaps that form unstable foam.

It is clear that design of a gypsum panel includes many variables thatare interrelated. Dispersants used to reduce water also change the settime of the gypsum slurry. Some dispersants stabilize foam bubbles,while other dispersants destabilize the foam. Set accelerators thatdecrease the initial hydration time also reduce initial fluidity of theslurry. In addition to changing bubble size distribution, soaps affectslurry fluidity. The additives used to control the slurry fluidity,hydration time and foam bubble size distribution each affect multiplevariables, making it difficult to strike a balance among all of thesefactors.

SUMMARY OF THE INVENTION

One or more of these and other problems are solved by each of theembodiments of the panel provided by the invention that includes amatrix of calcium sulfate dihydrate crystals and two different types ofdispersants. One dispersant is a dispersant component (hereafter“dispersant component”) and another dispersant is a polycondensationcomponent (hereafter referred to as the “polycondensation component”).The dispersant component has dispersing properties and is acomb-branched polymer with polyether side chains, naphthalenesulfonate-formaldehyde condensate, melamine sulfonate-formaldehydecondensate or mixture of two or more thereof. The polycondensationcomponent includes three repeating units. A first polycondensationrepeating unit has a polyether side chain and either an aromaticsub-unit or a heteroaromatic sub-unit. A second polycondensationrepeating unit has a OP(OH)₂ group and either an aromatic sub-unit or aheteroaromatic sub-unit. A third polycondensation repeating unit has anaromatic sub-unit or a heteroaromatic sub-unit. The secondpolycondensation repeating unit and the third polycondensation repeatingunit differ exclusively in that the OP(OH)₂ (“phosphate”) groups of thesecond polycondensation repeating unit are replaced by H in the thirdpolycondensation repeating unit, and the third polycondensationrepeating unit is not the same as the first polycondensation repeatingunit.

A method of making the gypsum panel includes combining stucco, water anda first dosage of a first dispersant to form a slurry. A second dosageof a second dispersant is added to the slurry. Properties of the gypsumslurry are tested and it is formed into a product. The product sets andproperties of the product are identified. The first dosage or the seconddosage is changed based on the properties of the slurry or product.

Using both types of dispersants brings to a panel product the advantagesof both. The dispersant component has greater efficacy for waterreduction than the polycondensation component, while thepolycondensation component minimizes the set retardation of the gypsumslurry. Simultaneous use of both dispersant types allows theseproperties to be balanced over a wide range of variables, including thesource and quality of raw materials, stucco crystal form, the number andamounts of other additives used. Manufacturing plants using differentraw materials are able to utilize a different ratio of the dispersantcomponent to the polycondensation component. Use of the two dispersantsalso allows for production of a cost effective product depending on thecosts of fuel and raw materials, and/or increased production rate.

In slurries additionally including foam to produce foam voids in thepanel products, surprisingly, it has also been found that the choice ofsome of the dispersant components allows for better control of the foamvoid structure in gypsum panel products. Some of the dispersantcomponents have minimal effect on the size and distribution of the foamvoids left behind by the foam added to the gypsum slurry, while otherdispersant components produce a noticeable effect. This effect is causedby the additives' effects upon the stability of the foam. The ability tochoose the dispersant types and proportions to achieve a desired degreeof foam stability would provide another means of engineering anappropriate foam void structure to provide desired balance of strengthand density to the gypsum panel product.

Optionally, the panel also includes a defoaming component to have afurther effect on achieving the desired balance. The defoaming componentis present either as a free compound in solution or as a moiety on thedispersant component or the polycondensation component.

The method of adjusting the relative amounts of two dispersants relativeto each other adds another degree of freedom in the process control.Properties such as the slurry fluidity, the hydration time and the foambubble size are affected by a number of additives. Balancing amounts ofset accelerator, dispersant, foaming agent, antifoaming agent and thelike makes it difficult to achieve the desired properties. Selection ofdispersants that promote different effects in the properties provides away of achieving the desired hydration time, bubble size distributionand fluidity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of the interior of a sample having void StructureA;

FIG. 2 is a photograph of the interior of a sample having void StructureB;

FIG. 3 is a photograph of the interior of a sample having void StructureC;

FIG. 4 is a graphic representation of the amount of dispersant fromTable 1 used at various water to stucco ratios using several differentdispersant ratios;

FIG. 5 is a graphic representation of the amount of dispersant used atvarious amounts of set accelerator for several different dispersantratios; and

FIG. 6 is a graphic representation of the ratio of soap that producesunstable foam to soap that produces stable foam at various water tostucco ratios for several different dispersant ratios.

DETAILED DESCRIPTION OF THE INVENTION

Gypsum panels are made from a slurry on high-speed manufacturingequipment. Efficient manufacturing of gypsum slurries or panels requirescontrol over the product properties. A gypsum panel including additivesand a method for adjusting these additives provides improved controlover the manufacturing process and an improved product.

As used herein, “efficacy” is a measure of a dispersant's ability toimprove the fluidity of a gypsum slurry at constant dispersant dosage.If improved fluidity is not needed, improvements in efficacy can be usedto reduce the amount of water used to fluidize the slurry while holdingthe fluidity, or “slump,” constant. A decision as to which of thesechoices to select is based on a number of things including the productto be made, the raw materials, process configurations and economics.

“Hydration time” is a measure of the rate of the hydration reactions. Insome manufacturing facilities, it is important to achieve a sufficientdegree of hydration, or “set”, in the time it takes the gypsum to arriveat the knife, such that the panels have enough stiffness to maintaintheir structural integrity. The knife cuts the gypsum ribbon intoindividual panels.

“Gypsum bubble structure” refers to the sizes of individual bubbles inthe slurry after the foam has been added. It should be understood thatthe foam bubbles in the slurry form the foam voids in the set gypsumpanel when the calcium sulfate dihydrate crystals form around the foambubble. Thus, the sizes of the foam voids are determined by the sizes ofthe bubbles from which they are made. Various types of structures areoften utilized in panels, each of which can be desirable in differentproducts. FIGS. 1, 2 and 3 illustrate some of these various structures,denoted Structure A, Structure B and Structure C, respectively. Thesestructures vary in their foam void size, proceeding in size going fromStructure A to Structure B to Structure C.

A gypsum building panel is made using stucco and water to form a calciumsulfate dihydrate crystal matrix. Stucco is an inorganic binder materialalso known as calcined gypsum, calcium sulfate hemihydrate, calciumsulfate anhydrite or plaster of Paris. Synthetic gypsums, such as thatformed as a by-product of flue gas desulfurization, are also useful. Anyof the several forms of stucco are useful in the building panel of thepresent invention, including alpha or beta-calcined gypsum or mixturesthereof. A needle-shaped crystal of beta-stucco is formed by calcinationat atmospheric pressure. Alpha-calcined stucco is produced when gypsumis calcined under pressure and is characterized by less acyclicalcrystals. Beta-calcined stucco requires more water than alpha-calcinedstucco to make a slurry of equivalent flowability. Upon the addition ofwater, all forms of the stucco hydrate to form an interlocking matrix ofcalcium sulfate dihydrate crystals.

Addition of other inorganic binder components together with the stuccois contemplated for use with the present panel, including, but notlimited to cement, pozzolans, gypsum and combinations thereof. In someembodiments the calcined gypsum is present in the slurry in amounts ofmore than 50% by weight of the total inorganic binder components.

Water is added to the stucco in sufficient amounts to make a flowableslurry. The water to stucco ratio (“WSR”) is the weight of water perhundred weight dry stucco. A WSR of about 20 is the minimum amount ofwater needed to fully hydrate calcium sulfate hemihydrate. Someembodiments of the invention utilize a WSR from about 20 to about 100.Other embodiments have a WSR from about 40 to about 70. The amount ofwater required will depend on the type of calcined gypsum, the type ofadditives used, the stucco source and the quantity of the additives thatare utilized.

In addition to the stucco and water, the slurry utilized for someembodiments is made using two dispersants. Preferably the twodispersants include any dispersant and a polycondensation component. Insome aspects of the invention, the dispersant is a dispersant componentfurther described below. The slurry optionally includes additionalcomponents such as surfactants and antifoaming agents.

The dispersant component has one or more dispersant properties. Anydispersing properties known in the art are suitable. Examples ofdispersing properties include, but are not limited to increasedflowability, slurry uniformity and reduction in water addition. Thedispersant component is selected from a group that includescomb-branched polymers having polyether side chains, naphthalenesulfonate-formaldehyde condensates, melamine sulfonate-formaldehydecondensates and mixtures thereof. Preferably, from 0.05 to 1.0 wt. %,preferably from 0.1 to 0.5 wt. % and especially preferably from 0.15 to0.3 wt. % of the additive blend is the dispersant component, each basedon the total additive blend.

Formulations which contain a comb-branched polymer having polyether sidechains as the dispersant component have been found to be effective.Examples of the dispersant component include a polycarboxylate ether, apolycarboxylate ester, an uncharged copolymer or a mixture thereof.

Polycarboxylate ether copolymers which are suitable as the dispersantcomponent have been previously described in WO 2006/133933 A2, hereinincorporated by reference. These copolymers consist of two repeatingunits. The first polycarboxylate repeating unit is derived from anolefinically unsaturated monocarboxylic acid comonomer, an ester or asalt thereof and/or an olefinically unsaturated sulfonic acid comonomeror a salt thereof.

The second polycarboxylate repeating unit is of the general formula (I)

wherein R₁ represents

and R₂ represents H or an aliphatic hydrocarbon residue with 1 to 5 Catoms; R₃=unsubstituted or substituted aryl residue and preferablyphenyl, and R₄═H or an aliphatic hydrocarbon residue with 1 to 20 Catoms, cycloaliphatic hydrocarbon residue with 5 to 8 C atoms, asubstituted aryl residue with 6 to 14 C atoms or a member of the series:

wherein R₅ and R₇ each represent an alkyl, aryl, aralkyl, or alkarylresidue and R₆ for an alkylidene, arylidene, aralkylidene oralkarylidene residue, and

p=0, 1, 2, 3 or 4

m, n mutually independently mean 2, 3, 4 or 5

x and y mutually independently denote an integer≦350

and z 0 to 200.

In some embodiments, there are no internal molecular differences betweenthe first polycarboxylate repeating unit and the second polycarboxylaterepeating unit in polycarboxylate ether copolymer. Other embodiments ofthe copolymer utilize a polymeric mixture of the first polycarboxylaterepeating unit and the second polycarboxylate repeating unit, in whichcase there are optionally internal molecular differences with respect tothe radicals R¹, R², R³, R⁴, R⁵, R⁶, R⁷, m, n, x, y and/or z. Thedifferences often relate to the composition and length of the sidechains.

The polycarboxylate ether copolymer includes the first polycarboxylaterepeating unit in amounts of about 30 to about 99 mol. % and the secondpolycarboxylate repeating unit in amounts of about 70 to about 1 mol. %.Embodiments where the polycarboxylate ether copolymer includes the firstpolycarboxylate repeating unit in proportions of about 40 to about 90mol. % and the second polycarboxylate repeating unit in amounts of about60 to about 10 mol. % has been found particularly advantageous.

The first polycarboxylate repeating unit is preferably derived from anacrylic acid or a salt thereof and the second polycarboxylate repeatingunit is derived from a monomer component that is preferably a vinyl orallyl group having as the residue R¹ a polyether and where p=0 or 1.Further, in some embodiments the first polycarboxylate repeating unitsderive from acrylic acid, methacrylic acid, crotonic acid, isocrotonicacid, allylsulfonic acid, vinylsulfonic acid and suitable salts thereofand alkyl or hydroxyalkyl esters thereof.

In addition, the polycarboxylate ether copolymer optionally hasadditional structural groups in copolymerized form. In this case, theadditional structural groups that include styrenes, acrylamides,hydrophobic compounds, ester repeating unit, polypropylene oxide andpolypropylene oxide/polyethylene oxide units are preferred. Thepolycarboxylate ether copolymer includes the additional repeating unitsin amounts up to 5 mol. %, preferably from 0.05 to 3.0 mol. % and morepreferably from 0.1 to 1.0 mol. %.

Any comb-branched polycarboxylate dispersant is useful in the slurry.Examples of useful polycarboxylate dispersants include, but are notlimited to dispersants from the MELFLUX® Dispersant series by BASFConstruction Polymers, GmbH (Tröstberg, Germany), ETHACRYL® M Dispersantby CoAtex, LLC (Chester, S.C.) and MIGHTY EG® Dispersant by KaoSpecialties Americas, LLC, (High Point, N.C.). The use of combinationsof dispersants is also contemplated. All of these polymers havepolyether side chains.

Suitable polycarboxylate esters are included in EP 0 753 488 B1, hereinincorporated by reference. The polycarboxylate ester in some embodimentsis prepared by polymerization of a monomer mixture containing acarboxylic acid monomer as the main component. In other embodiments, itis advantageous if the formula (I) represents a polyether containingalkyl or vinyl groups. An aspect of many polycarboxylate esters is theiranti-foaming, defoaming and/or surface active properties. Therefore insome embodiments where the dispersant component is such apolycarboxylate ester, the dispersant component can provide antifoamingand surfactant effects in addition to their dispersing effect. In someembodiments, the monomer mixture includes an (alkoxy)polyalkylene glycolmono(meth)acrylate monomer of the general formula (II):

in which R¹ represents a hydrogen atom or a CH₃ group, R²O representsone representative or a mixture of at least two oxyalkylene groupshaving 2 to 4 carbon atoms, R³ represents a hydrogen atom or an alkylgroup having 1 to 5 carbon atoms and m represents a number between 1 and250 and represents the average number of moles of the oxyalkylene groupadded,

A second monomer is a (meth)acrylic acid of the general formula (III),

in which R⁴ represents a hydrogen atom or a CH₃ group and M¹ representsa hydrogen atom, a monovalent metal atom, a divalent metal atom, anammonium group or an organic amine group.

An additional monomer is optionally copolymerized with the carboxylicacid monomers and the (meth)acrylic acid monomers. The carboxylic acidmonomers are preferably present in an amount of from about 5 to about 98wt. %, the (meth)acrylic acid monomers in an amount of from about 2 toabout 95 wt. % and the optional monomer in an amount of up to about 50wt. % in the monomer mixture (I).

Typical representatives of the polycarboxylate monomer includehydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, polyethyleneglycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate,polybutylene glycol mono(meth)acrylate, polyethylene glycolpolypropylene glycol mono(meth)acrylate, polyethylene glycolpolybutylene glycol mono(meth)acrylate, polypropylene glycolpolybutylene glycol mono(meth)acrylate, polyethylene glycolpolypropylene glycol polybutylene glycol mono(meth)acrylate,methoxypolyethylene glycol mono(meth)acrylate, methoxypolypropyleneglycol mono(meth)acrylate, methoxypolybutylene glycolmono(meth)acrylate, methoxypolyethylene glycol polypropylene glycolmono(meth)acrylate, methoxypolyethylene glycol polybutylene glycolmono(meth)acrylate, methoxypolypropylene glycol polybutylene glycolmono(meth)acrylate, methoxypolyethylene glycol polypropylene glycolpolybutylene glycol mono(meth)acrylate, ethoxypolyethylene glycolmono(meth)acrylate, ethoxypolypropylene glycol mono(meth)acrylate,ethoxypolybutylene glycol mono(meth)acrylate, ethoxypolyethylene glycolpolypropylene glycol mono(meth)acrylate, ethoxypolyethylene glycolpolybutylene glycol mono(meth)acrylate, ethoxypolypropylene glycolpolybutylene glycol mono(meth)acrylate, ethoxypolyethylene glycolpolypropylene glycol polybutylene glycol mono(meth)acrylate or mixturesthereof.

For the (meth)acrylic acid monomer, acrylic acid, methacrylic acid,monovalent metal salts, divalent metal salts, ammonium salts and organicamine salts thereof and mixtures thereof are to be regarded aspreferred.

As regards the additional optional monomer, it has an ester of analiphatic alcohol with 1 to 20 carbon atoms and an unsaturatedcarboxylic acid. The unsaturated carboxylic acid is preferably maleicacid, fumaric acid, citraconic acid (meth)acrylic acid or monovalentmetal salts, divalent metal salts, ammonium salts or organic amine saltsthereof.

The polycarboxylate ester of the comb-branched polymer can be acopolymer which is made from at least one of the following monomers:

A) a first ethylenically unsaturated monomer containing a hydrolyzableresidue;

B) a second ethylenically unsaturated monomer with at least one C₂-C₄oxyalkylene side group with a chain length from 1 to 30 units; or

C) a third ethylenically unsaturated monomer with at least one C₂-C₄oxyalkylene side group with a chain length from 31 to 350 units.

In a preferred embodiment of the present invention the second and thirdethylenically unsaturated monomers are both present in thepolycarboxylate ester.

The first ethylenically unsaturated monomer is at least one anhydride orimide and/or at least one maleic anhydride or maleimide. The firstethylenically unsaturated monomer also optionally includes an acrylateester with an ester functionality which contains the hydrolyzableresidue. In this case, it should be regarded as preferred if the esterfunctionality is at least one hydroxypropyl or hydroxyethyl radical.

In a further embodiment the polycarboxylate ester can further includemore than one ethylenically unsaturated monomer with a hydrolyzableradical. Preferably the first ethylenically unsaturated monomer has morethan one of the first ethylenically unsaturated monomers, at least onerepresentative of a hydrolyzable radical or a mixture of both. In thiscase, the hydrolyzable radical should have at least one C₂-C₂₀ alcoholfunctionality. The present invention also includes the possibility thatthe hydrolyzable residue is at least one C₁-C₂₀ alkyl ester, one C₁-C₂₀aminoalkyl ester, one C₂-C₂₀ alcohol, one C₂-C₂₀ amino alcohol or oneamide.

At least one of the second or third ethylenically unsaturated monomerhas a C₂-C₈ alkyl ether group. In this case, the ethylenicallyunsaturated monomer can have a vinyl, allyl or (methyl)allyl etherresidue or else be derived from an unsaturated C₂-C₈ alcohol. In thelatter case of the unsaturated C₂-C₈ alcohol, at least vinyl alcohol,(meth)allyl alcohol, isoprenol or methylbutanol are especially preferredpossibilities as representatives. The ethylenically unsaturated monomerside groups of the second or third ethylenically unsaturated monomer canhowever also contain at least one C₄ oxyalkylene unit.

In connection with the modifications just described, concerning thepolycarboxylate ester comb-branched polymer, it can be stated that atleast one of the second and third ethylenically unsaturated monomersoptionally has a C₂-C₈ carboxylate ester which in particular ishydrolyzable. Further, the oxyalkyl side groups have at least oneethylene oxide, one propylene oxide, one polyethylene oxide, onepolypropylene oxide or mixtures thereof.

Finally, the polycarboxylate ester copolymer optionally includes atleast one nonionic (“uncharged”) monomer, one non-hydrolyzable monomerresidue or mixtures thereof.

In addition to the polycarboxylate ethers and polycarboxylate esters,the present invention also includes a fourth polycarboxylate repeatingunit of the comb-branched polymer which is a nonionic copolymer. Unitsof the general formula (IV) are preferred for forming the nonioniccopolymer:

wherein Q stands for an ethylenically unsaturated monomer with at leastone hydrolyzable residue, G means O, C(O)—O or O—(CH₂)_(p)—O with p=2 to8, wherein mixtures of the modifications of G in one polymer arepossible; R¹ and R², independently, are at least one C₂-C₈ alkyl; R³comprises (CH₂)_(c), where c is a whole number between 2 and 5 and wheremixtures of the representatives of R³ in the same polymer molecule arepossible; R⁵ means at least one representative selected from the seriesH, a linear or branched, saturated or unsaturated C₁-C₂₀ aliphatichydrocarbon residue, a C₅-C₈ cycloaliphatic hydrocarbon residue or asubstituted or unsubstituted C₆-C₁₄ aryl residue; m=1 to 30, n=31 to350, w=1 to 40, y=0 to 1 and z=0 to 1, where the sum (y+z)>0,

The nonionic copolymer alternatively includes units of the generalFormula (V):

wherein X stands for a hydrolyzable residue and R for H or CH₃, and G,p, R¹, R², R³, R⁵, m, n, w, y, z and (y+z) have the meanings statedunder the formula (IV).

In the case where the structure of the nonionic copolymer corresponds toFormula (V), in a preferred embodiment the hydrolyzable residue is atleast one representative of the series alkyl ester, aminoalkyl ester,hydroxyalkyl ester, aminohydroxyalkyl ester or amide.

The nonionic copolymer can also be of the general formula (VI):

wherein R⁴ is at least one C₁-C₂₀ alkyl or a C₂-C₂₀ hydroxyalkylradical, and the variables G, p, R, R¹, R², R³, c, R⁴, R⁵, m, n, w, y, zand (y+z) have the meanings as defined for the nonionic copolymer above.

It is preferable that in Formula (VI), p=4, R⁴═C₂H₄OH or C₃H₆OH, each ofthe radicals R⁵ represents H, m=5-30, n=31-250, w=1.5-30, y=0 to 1, z=0to 1 and (y+z)>0. In another preferred embodiment, in Formulae (IV), (V)and (VI), the molar ratio of w to the sum (y+z) is 1:1 to 20:1 andpreferably 2:1 to 12:1. Another preferred embodiment of Formula (VI) isa nonionic polyether-polyester copolymer.

The dispersant component acts to increase the hydration time, with somepolycarboxylates causing severe set retardation. Most polycarboxylatedispersants stabilize foam. An exception to this is a polycarboxylatedispersant that includes an antifoaming component together with thedispersant.

Regardless of the specific dispersants or moieties that are selected,the dispersant component is optionally present in an additive blend inamounts of about 5% to about 95% by weight. In some embodiments thedispersant component is about 10% to about 60% or from about 15% toabout 40% by weight of the additive blend.

Sulfonated condensates are also useful as the dispersant component.Sulfonic acid group containing s-triazines or naphthalene-formaldehydecondensates are broadly disclosed by prior art documents and frequentlyused as water reducing agents or plasticizers for cement based systemssuch as concrete.

β-naphthalene-sulfonate-formaldehyde condensates (“BNS”), also known asnaphthalene-formaldehyde sulfonates, disperse particles by anelectrostatic repulsion that results from adsorption processes. Themolar ratio of formaldehyde to naphthalene sulfonic acid is from about1.3 to 1 to about 3 to 1.

It is well known that commercially available flow improving agents basedon melamine-formaldehyde-sulfonates, such as products of the MELMENT®series of dispersants from BASF Construction Polymers GmbH, Tröstberg,Germany, cause an excellent liquefying effect even of low dosages ofabout 0.3 to 1.2 wt. %, relative to the weight of an inorganic binder.

The BNS or MFS dispersant is used in amounts of from 0.01 to 10 wt. %and preferably 0.1 to 5 wt. %, related to the hydraulic bindercomponent. The molar ratio of the sulfonic group and related to themelamine component is of from 1.0 to 2.0 and the molar ratio of theformaldehyde related to the melamine component is from 2.5 to 5.0.Preferably the molar ratio melamine to sulfonic acid to formaldehyde is1:1.1:1.5:3.3:3.6. Both BNS and MFS dispersants destabilize foam andincrease fluidity in addition to increasing foam bubble structure.

The polycondensation component is also present in some embodiments. Thepolycondensation component is a copolymer having at least threepolycondensate repeating units. A first polycondensate repeating unithas an aromatic or heteroaromatic sub-unit and a polyether side chain. Asecond polycondensate repeating unit includes at least one phosphatedpolycondensate repeating unit having an aromatic or heteroaromaticsub-unit. A third polycondensate repeating unit has an aromatic orheteroaromatic sub-unit. The second polycondensate repeating unit andthe third polycondensate repeating unit differ exclusively in that theOP(OH)₂ group of the second polycondensate repeating unit is replaced byH in the third structural unit, and the third polycondensate repeatingunit is not the same as the first polycondensate repeating unit.

The first polycondensate repeating unit of the polycondensationcomponent is described by Formula (VII):

-   wherein A units are identical or different and are represented by a    substituted or unsubstituted aromatic or heteroaromatic compound    having 5 to 10 C atoms;-   where B units are identical or different and are represented by N,    NH or O;-   where n=2, if B═N and n=1, if B═NH or O;-   wherein R¹ and R², independently of one another, are identical or    different and are represented by a branched or straight-chain C₁- to    C₁₀-alkyl radical, C₅- to C₈-cycloalkyl radical, aryl radical,    heteroaryl radical or H;-   wherein “a” values are identical or different and are represented by    an integer from 1 to 300;-   wherein X units are identical or different and are represented by a    branched or straight-chain C₁- to C₁₀-alkyl radical, C₅- to    C₈-cycloalkyl radical, aryl radical, heteroaryl radical or H.

The second polycondensate repeating unit is described by Formula (VIII):

and the third polycondensate repeating unit is described by Formula(IX):

For Formulas (VIII) and (IX) in each case:D units are identical or different and are represented by a substitutedor unsubstituted heteroaromatic compound having 5 to 10 C atoms;E units are identical or different and are represented by N, NH or 0;m=2 if E=N and m=1 if E=NH or O;R³ and R⁴, independently of one another, are identical or different andare represented by a branched or straight-chain C₁- to C₁₀-alkylradical, C₅- to C₈-cycloalkyl radical, aryl radical, heteroaryl radicalor H;“b” values are identical or different and are represented by an integerfrom 0 to 300;M groups, independently of one another, are an alkaline metal ion,alkaline earth metal ion, ammonium ion, organic ammonium ion and/or H;andc is 1 or in the case of alkaline earth metal ions ½.

In a preferred embodiment, the polycondensation component contains afourth polycondensate repeating unit of Formula (X):

wherein Y groups, independently of one another, are identical ordifferent and are represented by Formulae (VII), (VIII), (IX) or furtherconstituents of the polycondensate;wherein R⁵ groups are identical or different and are represented by H,CH₃, COOM_(c) or a substituted or unsubstituted aromatic orheteroaromatic compound having 5 to 10 C atoms; andwherein R⁶ groups are identical or different and are represented by H,CH₃, COOM_(c) or a substituted or unsubstituted aromatic orheteroaromatic compound having 5 to 10 C atoms.

Preferably, R⁵ and R⁶ in Formula (X), independently of one another, arerepresented by H, COOM_(C) and/or methyl.

The molar ratio of the units of Formulae (VII), (VIII), (IX) and (X) ofthe polycondensation component varies within wide ranges. In someembodiments wherein the molar ratio of the first, second, third andfourth polycondensate repeating units are represented by their formulanumber, then [(VII)+(VIII)+(IX)]:(X) is 1:0.8 to 3, preferably 1:0.9 to2 and particularly preferably 1:0.95 to 1.2. The molar ratio of thefirst, second and third polycondensate repeating units(VII):[(VIII)+(IX)] in the polycondensation component is usually 1:15 to15:1, preferably 1:10 to 10:1 and more preferably 1:5 to 3:1. In apreferred embodiment, the molar ratio of the second and third repeatingunits (VIII):(IX) is adjusted to 1:0.005 to 1:10, preferrably 1:0.01 to1:1, in particular 1:0.01 to 1:0.2 and more preferably 1:0.01 to 1:0.1.

The groups A and D in the repeating units of Formulae (VII), (VIII) and(IX) of the polycondensation component are preferably represented byphenyl, 2-hydroxyphenyl, 3-hydroxyphenyl, 4-hydroxyphenyl,2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, naphthyl,2-hydroxynaphthyl, 4-hydroxynaphthyl, 2-methoxynaphthyl,4-methoxynaphthyl, preferably phenyl. It is possible for A and D to bechosen independently of one another and also in each case to consist ofa mixture of said compounds. The groups B and E, independently of oneanother, are preferably represented by an oxygen atom, O.

The radicals R¹, R², R³ and R⁴ can be chosen independently of oneanother and are preferably represented by H, methyl, ethyl or phenyl,particularly preferably by H or methyl and especially preferably by H.

Value a in the first polycondensation repeating unit of Formula (VII) ispreferably represented by an integer from 5 to 280, in particular 10 to160 and particularly preferably 12 to 120. Value b in the second andthird repeating units (VIII) and (IX) is an integer from 0 to 10,preferably 1 to 7 and particularly preferably 1 to 5. The respectiveradicals, the length of which is defined by a and b, respectively, mayconsist of uniform building blocks, but a mixture of different buildingblocks may also be expedient. Furthermore, the radicals of the first,second and third repeating units of Formulae (VII) or (VIII) and (IX),independently of one another, may each have the same chain length, a andb each being represented by a value. It is preferred that mixtureshaving different chain lengths are present in each case so that theradicals of the repeating units in the polycondensate have differentnumerical values for a and, independently, for b.

Frequently, the phosphated polycondensate component has a weight averagemolecular weight of 4000 g/mol to 150 000 g/mol, preferably 10 000 to100 000 g/mol and particularly preferably 20 000 to 75 000 g/mol.

Preferably, the phosphated polycondensation component is added to theslurry as an aqueous solution which contains about 2 to about 90% byweight of water and about 98 to about 10% by weight of dissolved drymatter, preferably about 40 to about 80% by weight of water and about 60to about 20% by weight of dissolved dry matter, and more preferablyabout 45 to about 75% by weight of water and about 55 to about 25% byweight of dissolved dry matter. If desired other soluble, dry additivescan also be dissolved in the same solution for convenient addition tothe slurry, such as antifoaming agents.

In a particular embodiment, the invention furthermore contemplates asodium, potassium, ammonium and/or calcium salt and preferably a sodiumand calcium salt, of the phosphated polycondensation component.

A process for the phosphation of the polycondensation component isoptionally carried out in the reaction mixture. This is to be understoodas meaning that the phosphated polycondensation component formed in thereaction solution needs neither be purified nor isolated. Thephosphation can be carried out before, during or after thepolycondensation. Preferably both the phosphation and thepolycondensation are carried out in the same reaction vessel.

In a preferred embodiment, the reaction mixture for synthesis of thepolycondensation component includes at least a monomer of the firstpolycondensation repeating unit, a monomer of the third polycondensationrepeating unit, and a further monomer having an aldehyde group and aphosphating agent. The monomer of the third polycondensation repeatingunit is not the same as the monomer of the first polycondensationrepeating unit. A portion of the monomer of the third polycondensationrepeating unit is partially phosphated during the reaction and forms themonomer of the second polycondensation repeating unit as shown inFormula (VIIIa.) Each of the variables is defined in the same manner asfor the corresponding polycondensation repeating unit above.

where R⁷ units are identical or different and are represented by H, CH₃,COOH and/or a substituted or unsubstituted aromatic or heteroaromaticcompound having 5 to 10 C atoms; and where R⁸ units are identical ordifferent and are represented by H, CH₃, COOH and/or a substituted orunsubstituted aromatic or heteroaromatic compound having 5 to 10 Catoms.

The present invention provides different variants of the reactionprocedure. One possibility consists of first reacting the monomer of thethird polycondensation repeating unit with a phosphating agent andsubjecting the monomer of the second polycondensation repeating unitthus obtained to polycondensation with the monomers of the first andthird polycondensation repeating units and the monomer of the fourthrepeating unit. The monomer of the third polycondensation repeating unitmay be present from an incomplete reaction during the phosphationreaction or can be deliberately added to the reaction mixture after thephosphation reaction.

However, it is also possible to subject the monomers of the first andthird polycondensation repeating units and the further monomer topolycondensation and then to react the polycondensate product obtainedwith a phosphating agent. In another embodiment, the monomers of thefirst and third polycondensation repeating units, the monomer of thefourth repeating unit and the phosphating agent are reactedsimultaneously. Polyphosphoric acid and/or phosphorous pentoxide aresuitable phosphating agents. The polycondensation is carried out in thepresence of an acidic catalyst, this preferably being sulfuric acid,methanesulfonic acid, para-toluenesulfonic acid or mixtures thereof.

The polycondensation and the phosphation are advantageously carried outat a temperature between 20 and 140° C. and a pressure between 1 and 10bar. In particular, a temperature range between 80 and 110° C. hasproved to be useful. The duration of the reaction may be between 0.1 and24 hours, depending on temperature, the chemical nature of the monomersused and the desired degree of crosslinking. Once the desired degree ofcrosslinking has been reached, which can also be determined, forexample, by measurement of the viscosity of the reaction mixture, thereaction mixture is cooled.

According to a particular embodiment, the reaction mixture is subjectedto a thermal aftertreatment at a pH between 8 and 13 and a temperaturebetween 60 and 130° C. after the end of the condensation and phosphationreaction. As a result of the thermal aftertreatment, whichadvantageously lasts for between 5 minutes and 5 hours, it is possiblesubstantially to reduce the aldehyde content, in particular theformaldehyde content, in the reaction solution.

In a further particular embodiment, the present invention envisagessubjecting the reaction mixture to a vacuum aftertreatment at pressuresbetween 10 and 900 mbar after the end of the condensation andphosphation reaction, for reducing the aldehyde content. Other methodsknown to the person skilled in the art for reducing the formaldehydecontent may also be used. An example is the addition of small amounts ofsodium bisulfite, ethylene urea or polyethylenimine.

The phosphated polycondensates obtained by these processes can be useddirectly as the polycondensation component. In order to obtain a bettershelf life and better product properties, it is advantageous to treatthe reaction solutions with basic compounds. Preferably the reactionmixture is treated after the end of the polycondensation reaction with abasic sodium, potassium, ammonium or calcium compound. Sodium hydroxide,potassium hydroxide, ammonium hydroxide or calcium hydroxide areparticularly useful, since it is preferred to neutralize the reactionmixture. Other alkali metal and alkaline earth metal salts and salts oforganic amine are suitable as salts of the phosphated polycondensatecomponents.

Mixed salts of the phosphated polycondensation components are preparedby reacting the polycondensates with at least two basic compounds. Thus,by a targeted choice of suitable alkali metal and/or alkaline earthmetal hydroxides, it is possible by neutralization to prepare salts ofthe polycondensation components, with which the duration of theprocessability of aqueous suspensions of inorganic binders and inparticular of concrete can be influenced. While a reduction in theprocessability over time is observable in the case of the sodium salt, acomplete reversal of this behavior takes place in the case of thecalcium salt of the identical polymer, a smaller water reduction(smaller slump) occurring at the beginning and increasing with time. Asa result of this, sodium salts of the phosphated polycondensationcomponents lead to a decrease in the processability over time of thebinder-containing material, such as, for example, concrete, mortar orgypsum slurries, whereas the corresponding calcium salts lead with timeto improved processability. By suitable choice of the amount of sodiumand calcium salts of the phosphated polycondensates used, thedevelopment of the processability of binder-containing materials canthus be controlled as a function of time. Expediently, the correspondingphosphated polycondensation components, which consist of sodium andcalcium salts, are prepared by reaction with a mixture of basic calciumand sodium compounds, in particular calcium hydroxide and sodiumhydroxide.

According to the present invention, a catalyst used can also beseparated off. This can expediently be affected via the salt formedduring the neutralization. If sulfuric acid is used as the catalyst andthe reaction solution is treated with calcium hydroxide, the calciumsulfate formed can be separated off, for example, in a simple manner byfiltration. Furthermore, by adjusting the pH of the reaction solution to1.0 to 4.0, in particular 1.5 to 2.0, the phosphated polycondensationcomponent is separated from the aqueous salt solution by phaseseparation and can be isolated. The phosphated polycondensationcomponent can then be taken up in the desired amount of water. Othermethods known to the person skilled in the art, such as dialysis,ultrafiltration or the use of an ion exchanger, are also suitable forseparating off the catalyst.

Additionally, it is advantageous that the methods of making thephosphated polycondensation components can be prepared by a veryeconomical process, with no further purification of intermediates beingrequired. In particular, no wastes which have to be disposed of form inthe process according to the invention. Thus, the claimed process alsoconstitutes further progress compared with the prior art fromenvironmental points of view. The reaction mixture obtained can be putdirectly to the intended formulation optionally after treatment withbasic compounds.

In a specific embodiment the slurry includes the dispersant component,the polycondensation components, at least one antifoaming agent and/or acomponent having a surface-active effect, the antifoaming agent andcomponent having a surface-active effect being structurally differentfrom one another.

The antifoaming agent is preferably selected from the group consistingof a mineral oil, a vegetable oil, a silicon oil, a silicon containingemulsion, a fatty acid, a fatty acid ester, an organic modifiedpolysiloxane, a borate ester, an alkoxylate, a polyoxyalkylenecopolymer, ethylene oxide (EO)-propylene oxide (PO) block polymer,acetylenic dials having defoaming properties and a phosphoric esterhaving the formula P(O)(O—R⁸)_(3-x)(O—R⁹)_(x) where P representsphosphorus, O represents oxygen and R⁸ and R⁹ are, independently, aC₂-C₂₀ alkyl or an aryl group and x=0, 1, 2, whereby an alkyl group withC₂-C₈ is preferred. Preferably the antifoaming agent includestri-alkylphosphate and more preferably triiso-butylphosphate, apolyoxypropylene copolymer and a glycerol/alcohol acetate. Anotherembodiment of the slurry includes a mixture where the antifoaming agentincludes a mixture of a tri-alkylphosphate and a polyoxypropylenecopolymer.

The second optional component of the formulation, namely the surfactant,is preferably selected from the group consisting of a ethyleneoxide/propylene oxide (EO/PO) block copolymer, a styrene/maleic acidcopolymer, a fatty alcohol alkoxylate, an alcohol ethoxylate R₁₀—(EO)—Hwith R₁₀ being an aliphatic hydrocarbon group having from 1 to 25 carbonatoms, acetylenic dials, monoalkylpolyalkylenes, ethoxylatednonylphenols, alkylsulfates, alkylethersulfats, alkylethersulfonates,alkyl ether carboxylates. More preferably the surfactant componentincludes an alcohol having a polyalkylene group of a carbon chain lengthof 2 to 20 carbon atoms, with a preferred carbon chain length of C₃-C₁₂.

Prior to addition to the gypsum slurry, the dispersant component and thepolycondensation component are optionally pre-mixed in an aqueouscomposition that includes the antifoaming agent component in free formand/or chemically or physically attached to the dispersing componentand/or the polycondensation component. Any or all of these componentscan be added directly to the gypsum slurry without pre-blending.

In a further embodiment the antifoaming component is present in amountsof about 0.0002 to about 0.02% by weight and/or the surface-activecomponent is present in amounts of about 0.0002 to about 0.02% byweight, based in each case on the total weight of the dry dispersants.

In another optional embodiment, in addition to the dispersingcomponents, the polycondensation component and optionally theantifoaming agent or the surface-active component the slurry has atleast one further compound. The further compound is preferably a polymerhaving a low charge, a neutral polymer or polyvinyl alcohol. Thisfurther compound and its role in systems containing calcium sulfate ashydraulic binder has been taught in the unpublished provisional EuropeanPatent application EP 08171022.0, herein incorporated by reference. Thefurther compound is useful with gypsum compositions having certain claycontents.

The total concentration of the dispersant component and polycondensationcomponent to be included in the slurry ranges from 0.0002 to 1.6% byweight of the inorganic binder, or ranges from 0.001 to 1.0% by weight.In some embodiments, ranges from 0.002 to 0.4% by weight can beutilized. Other embodiments utilize 0.01 to 1.0% by weight or 0.05 to0.2% by weight. The ratio of the dispersant component to thepolycondensate component ranges from about 1:99 to about 99:1.

Additional additives are also added to the slurry as are typical for theparticular application to which the gypsum slurry will be put. Amountsof some additives are reported in pounds per 1000 ft² of board (“MSF”),based on a ½ inch (12 mm) gypsum panel.

Dry accelerators (up to about 35 lb./MSF (170 g/m2)) are added to modifythe rate at which the hydration reactions take place. “CSA” is a setaccelerator comprising 95% calcium sulfate dihydrate co-ground with 5%sugar and heated to 250° F. (121° C.) to caramelize the sugar. CSA isavailable from USG Corporation, Southard, Okla. plant, and is madeaccording to U.S. Pat. No. 3,573,947, herein incorporated by reference.Potassium sulfate, aluminum sulfate and sodium bisulfate are alsosuitable accelerators. HRA is calcium sulfate dihydrate freshly groundwith sugar at a ratio of about 5 to 25 pounds of sugar per 100 pounds ofcalcium sulfate dihydrate. It is further described in U.S. Pat. No.2,078,199, herein incorporated by reference. Both of these are preferredaccelerators. Set accelerators decrease hydration time and decreasefluidity.

Another accelerator, known as wet gypsum accelerator or WGA, is also apreferred accelerator. A description of the use of and a method formaking wet gypsum accelerator are disclosed in U.S. Pat. No. 6,409,825,herein incorporated by reference. This accelerator includes at least oneadditive selected from the group consisting of an organic phosphoniccompound, a phosphate-containing compound or mixtures thereof. Thisparticular accelerator exhibits substantial longevity and maintains itseffectiveness over time such that the wet gypsum accelerator can bemade, stored, and even transported over long distances prior to use. Thewet gypsum accelerator is used in amounts ranging from about 5 to about80 pounds per thousand square feet (24.3 to 390 g/m²) of board product.A specific example of a set retarder in some embodiments of theinvention is Versenex 80, which is a pentasodiumdiethylenetriaminepentaacetate (Dow Chemical, Midland, Mich.).

Set retarders (up to about 2 lb./MSF (9.8 g/m²)) are optionally used toprevent crystal formation in the mixer and to delay thickening of thegypsum slurry. The addition of the set retarder results in improvedflowability of the slurry through the mixer because the thickening isdelayed. Thus the amount of water in the slurry can be reduced. Thiswater reduction effect is in addition to the water reduction effectprovided by the dispersants. This effect is observed when retarder isused in amounts as little as 0.008% by weight based on the weight of drycalcined gypsum.

In some embodiments of the invention, additives are included in thegypsum slurry to adjust one or more properties of the final product.Additives are used in the manner and amounts as are known in the art.Concentrations are reported in amounts per 1000 square feet of finishedboard panels (“MSF”). Reinforcing materials such as glass fibers areoptionally added to the slurry in amounts of up to 11 lb./MSF (54 g/m²).Up to 15 lb./MSF (73.2 g/m²) of paper fibers are also added to theslurry. Wax emulsions are added to the gypsum slurry in amounts up to 90lb./MSF (0.4 kg/m²) to improve the water-resistency of the finishedgypsum board panel. Sugars, such as dextrose, are used to improve thepaper bond at the ends of the boards. Polysiloxanes are used for waterresistance. If stiffness is needed, boric acid is commonly added. Fireretardancy can be improved by the addition of vermiculite. These andother known additives are useful in the present slurry and wallboardformulations.

Modifiers are known that increase the efficacy of polycarboxylatedispersants. They are described in detail in U.S. Pat. No. 7,608,347,herein incorporated by reference, and U.S. Pat. No. 7,767,019,previously incorporated by reference. When used in combination with thedispersant, the addition of modifiers allows the amount of dispersant tobe reduced to obtain a desired slump size or produces a greater slumpsize at the same dispersant dosage. Examples of suitable modifiers arelime, carbonates, hydroxides, phosphates, phosphonates and silicates.Lime and soda ash are used in some embodiments due to their reasonablecost and ready availability.

In embodiments of the invention that employ a foaming agent to yieldfoam voids in the set gypsum-containing product to provide lighterweight, any of the conventional foaming agents known to be useful inpreparing foamed set gypsum products can be employed. Many such foamingagents are well known and readily available commercially, e.g. theHYONIC line of soap products from GEO Specialty Chemicals, Ambler, Pa.Any foaming agents are useful alone or in combination with other foamingagents. Generally, soaps do not affect hydration time or fluiditydirectly. However, soap addition can reduce fluidity when small bubblesare produced that tightly pack together and resist flow.

An example of a combination includes a first foaming agent which forms astable foam and a second foaming agent which forms an unstable foam. Thefirst foaming agent is optionally a soap with an alkyl chain length of8-12 carbon atoms and an ethoxy group chain length of 1-4 units. Thesecond foaming agent is optionally an unethoxylated soap with an alkylchain length of 6-16 carbon atoms. Regulating the respective amounts ofthese two soaps allows for control of the panel foam void structureuntil 100% stable soap or 100% unstable soap is reached. Foams and apreferred method for preparing foamed gypsum products are disclosed inU.S. Pat. No. 5,643,510, herein incorporated by reference.

If foam is added to the product, the polycarboxylate dispersant isoptionally divided between the gauging water and the foam water or twodifferent dispersants are used in the gauging water and the foam waterprior to its addition to the calcium sulfate hemihydrate. This method isdisclosed in co-pending application U.S. Ser. No. 11/152,404, entitled,“Effective Use of Dispersants in Wallboard Containing Foam”, previouslyincorporated by reference.

A trimetaphosphate compound is added to the gypsum slurry in someembodiments to enhance the strength of the product and to improve sagresistance of the set gypsum. Preferably the concentration of thetrimetaphosphate compound is from about 0.07% to about 2.0% based on theweight of the calcined gypsum. Gypsum compositions includingtrimetaphosphate compounds are disclosed in U.S. Pat. Nos. 6,342,284 and6,632,550, both herein incorporated by reference. Exemplarytrimetaphosphate salts include sodium, potassium or lithium salts oftrimetaphosphate, such as those available from Astaris, LLC., St. Louis,Mo. Care must be exercised when using trimetaphosphate with lime orother additives that raise the pH of the slurry. Above a pH of about9.5, the trimetaphosphate loses its ability to strengthen the productand the hydration rate of the slurry becomes severely lengthened.

Other potential additives to the wallboard are biocides to reduce growthof mold, mildew or fungi. Depending on the biocide selected and theintended use for the wallboard, the biocide can be added to thecovering, the gypsum core or both. Examples of biocides include boricacid, pyrithione salts and copper salts. Use of pryithione salts ingypsum panels are disclosed in U.S. Pat. No. 6,893,752, hereinincorporated by reference.

In addition, the gypsum composition optionally can include a starch,such as a pregelatinized starch or an acid-modified starch. Theinclusion of the pregelatinized starch increases the strength of the setand dried gypsum cast and minimizes or avoids the risk of paperdelamination under conditions of increased moisture (e.g., with regardto elevated ratios of water to calcined gypsum). One of ordinary skillin the art will appreciate methods of pregelatinizing raw starch, suchas, for example, cooking raw starch in water at temperatures of at leastabout 185° F. (85° C.) or other methods. Suitable examples ofpregelatinized starch include, but are not limited to, PCF 1000 starch,commercially available from Lauhoff Grain Company and AMERIKOR 818 andHQM PREGEL starches, both commercially available from Archer DanielsMidland Company. If included, the pregelatinized starch is present inany suitable amount. For example, if included, the pregelatinized starchcan be added to the mixture used to form the set gypsum composition suchthat it is present in an amount of from about 0.5% to about 10% percentby weight of the set gypsum composition. Pregelatinized starches such asUSG95 (United States Gypsum Company, Chicago, Ill.) are also optionallyadded for core strength.

Any of these components can be added in any of the ways components aretypically added to a gypsum slurry. Components may be added at thegauging water inlet, the dry additive inlet, the wet additive inlet, thedischarge conduit and even the vent for allowing excess air to escapethe mixer. The components may be added alone, together with other dryingredients, together with other wet ingredients, with the foam water,in the shear pump with other additives, or directly into the mixeralone. Some components may be pre-blended with each other or notpre-blended and added individually.

In operation, the calcined gypsum is moved on a conveyor toward a mixer.Prior to entry into the mixer, dry additives, such as dry setaccelerators, are added to the powdered calcined gypsum. Some additivesare added directly to the mixer via a separate line. Trimetaphosphate isoptionally added using this method. Other additives are optionally addeddirectly to the mixing or gauging water. This is particularly convenientwhere the additives are supplied in liquid form. For most additives,there is no criticality regarding placing the additives in the slurry,and they may be added using whatever equipment or method is convenient.When using some polycarboxylate dispersants, it is important to add thedispersant to the water prior to addition of the stucco.

The ingredients are mixed in a high shear mixer, such as a pin mixer,until a homogeneous slurry is obtained. Some slurries have no foamadded. In some embodiments, a foaming agent is added to the mixer andfoam is generated in situ during mixing, or pregenerated foam is addedto the mixer. In other embodiments, slurry is discharged into a conduitwhere, optionally, pregenerated foam is added to the slurry. Foam isoptionally added to the slurry by allowing it to flow over a foam ringhaving multiple foam outlets. This technique for foam addition isdiscussed in U.S. Pat. No. 5,683,635, herein incorporated by reference.After or during foam addition, the slurry travels down the conduit whereit is discharged as continuously onto a conveyor.

At or near the conveyor, a sample of the slurry is periodically taken totest the properties of the slurry and the set gypsum. A slump test isperformed to determine the fluidity of the slurry. The temperature risesetting time is determined in accordance with CSA A82.2OM 1977 PhysicalTesting of Gypsum Plasters, Section 5.3, herein incorporated byreference. Since hydration of calcined gypsum is an exothermic reaction,the temperature rise in the slurry from the initial mixing temperatureis indicative of the degree of set in the slurry.

Optionally, the conveyor is lined with a facing material onto which theslurry is deposited. Common facing materials include, but are notlimited to paper or cardboard having one or multiple plies, fiberglassmats, scrims and plastic films. A second facing material optionallycovers the slurry after it has been deposited to form a “sandwich” ofthe slurry between the two facing materials. The first facing materialcan be the same or different from the second facing material. Finishedpanels may include none, one or two facing materials. In someembodiments, a separate edge wrap material is placed on the edge facingsof the panel between the slurry and the facing material. Where no facingmaterial is used, the slurry is deposited directly onto the conveyorsurface.

After the slurry and any optional facing materials are in place on theconveyor, it is formed into a panel. The term “panel” is intended torefer to a piece of material having a thickness that is smaller thaneither the length or the width. The slurry mass passes under a screedbar at a forming station to spread the slurry evenly over the surface,to flatten the slurry and to make a continuous gypsum ribbon ofconsistent thickness. Commonly, the screed bar is set to thicknesses of½ (12 mm) or ⅝ (15 mm) of an inch, but thickness as small as ¼ inch (6mm) are known and panel thickness can exceed one inch (25 mm) inthickness. Edge formers smooth the edge of the slurry mass and fold theedge of the facing material, when present, to cover the edge. When theribbon has achieved a sufficient set strength, it is cut into lengths toform the panel. Preferably a surface of the panel is generallyrectangular in shape. To speed drying of the panels, they aretransferred into a kiln where they are dried at elevated temperatures.

At the knife where the panels are cut, a sample of the ribbon is takenperiodically to determine the void structure of the set gypsum. Thesample is cut or broken open to inspect the interior structure.

Based on the results of the production tests, adjustments are made inprocess parameters to improve the panel quality and/or manufacturingefficiency. If the hydration time is not at the target value, changes inprocess variables such as, the amount of set accelerator, the amount ofdispersant component or the amount of the polycondensate productcomponent are useful. Fluidity of the slurry is affected by at least theamount of set accelerator, the amount of the polycondensate productcomponent, the amount of the dispersant component and water. Whencorrection in the foam structure is required, adjustments can be made tothe amount of the dispersant component, the amount of the polycondensateproduct component, the amount of soap, the ratio of unstable to stablesoap and the amount of antifoaming agents used in the slurry.

Adjusting the relative amounts of the dispersant component and thepolycondensate component, or the relative amounts of any twodispersants, is useful in controlling one or more properties of thegypsum slurry or the resulting gypsum panel. A dispersant A and adispersant B are preferably different dispersant types as a variety ofrepeating units are more likely to have different effects on the gypsumslurry. Examples of dispersant types that could be used include thedispersant component and the polycondensate component described herein,formaldehyde condensates such as BNS and MFS dispersants.

To be most effective, the dispersants should affect the efficacy,fluidity and bubble structure of the gypsum slurry differently. This isnot to say that one dispersant need affect a given property in theopposite way as the other dispersant. One dispersant may have no effecton a property. However, the dispersants are selected to have effects ofdifferent magnitude with respect to the properties of interest. Forexample, some polycarboxylate ether dispersants strongly increase thefluidity of the slurry and tend to stabilize the bubbles. Naphthalenesulfonate dispersants increase fluidity to a lesser extent than thepolycarboxylate but tend to destabilize the bubbles. These twodispersants would be suitable for use in this process. Two dispersantsthat would not be suitable for use together would be those that have thesame effect on each property being considered. In this case, changingthe ratio of the dispersants would not result in a change in the processconditions.

Dispersants having additional repeating units or pendant groups that acton properties of the slurry are also suitable. Particularly, dispersantsare known to have antifoaming agents, surface-active groups or elementsthat assist the dispersant perform better in the presence of certainimpurities, such as clay contained in some stuccos.

Cases are also considered where either dispersant A, dispersant B orboth are blends of dispersants. The dispersant component and thepolycondensate component are available as a blend of these twodispersants. To obtain the ability to independently control the amountof the dispersant component relative to the polycondensate component,two different dispersant blends can be used. Here the dispersant blend Ais made of the dispersant component and the polycondensate in a ratio ofmore than 1:1 on a weight basis. The dispersant blend B is prepared withthe dispersant component and the polycondensate in a ratio of less than1:1 on a weight basis.

Dispersant A and dispersant B are then combined in different amounts tochange the ratio of the dispersant component to the polycondensatecomponent. Dispersants A and B are optionally combined prior to additionto the gypsum slurry. During the manufacture of the gypsum boards, therelative amounts of dispersant A and dispersant B are varied to obtainthe desired properties in response to the tests and observation of theslurry and panel product.

For example, consider a case where the dispersant component is a Melflux2661 type PCE comb-branched copolymer having polyether side chains(“dispersant A”) and where the dispersant component and thepolycondensate component (“dispersant B”) both include an antifoamingcomponent such that its characteristic is to destabilize the foam. Inthis example, the target core structure is void Structure B.

If the slump test indicates that the slurry is not as fluid, the amountof dispersant A can be increased to increase the slump. However,increasing the amount of dispersant A also increases the hydration timeand decreases the foam stability necessary to maintain void Structure B.To maintain the higher foam stability, the amount of soap that producesstable foam should be increased and the amount of soap that producesunstable foam should be decreased. Hydration time can be adjusted byvarying the amount of set accelerator.

In certain cases, it is not sufficient to vary only one of Dispersant Aor Dispersant B. If in the previous example, the manufacturing facilitywere already running at 100% stable soap, it would not be possible tovary the soap ratio alone to maintain the same bubble size distributionas from before the amount of Dispersant A were increased. The totalamount of soap that forms stable foam can be increased, however, the useof excessive amounts of soap causes problems in bonding of the gypsumpanel to the facing material and/or the formation of blisters.Similarly, it is possible that the retardation may be too extreme thatthe continued addition of set accelerator may not be able to control thehydration time. In cases such as these, it is beneficial also toindependently vary the amount of the Dispersant B, and thus the ratio ofthe dispersant component to the polycondensate component. Dispersant Baffects the fluidity almost as much as Dispersant A but has less of aneffect on the foam void size and the hydration time than Dispersant A.Changes that would need to be made in the slurry composition tocompensate for the effects of dispersant changes are reduced. Thistechnique is particularly helpful in cases where freedom to vary one ofthe other additives is limited. It should be noted that use of thetechnique is not limited to circumstances such as those discussed above.Varying the dispersant ratio should be considered any time it isnecessary to make corrections in the slurry or product properties.

Example 1 Synthesis of Polycondensation Component Example 1.1

A reactor equipped with a stirrer and a heating mantle is filled with600 parts of poly(ethyleneoxide)monophenylether (average molecularweight 5000 g/mol), 47.2 parts of concentrated methane sulfonic acid, 12parts of water, 110 parts of α-phenyl-ω-hydroxypoly(oxy-1,2-ethanediyl)phosphate (average molecular weight 368 g/mol) and 14.7 parts ofparaformaldehyde. This reaction mixture is stirred at 115° C. for 3hours. After cooling, 830 parts of water are added the reaction mixtureis neutralized with 50% sodium hydroxide solution to a pH value of 6.5to 7. The resin is a light yellow colored, clear and aqueous polymersolution with a solid concentration of 40% by weight. To the stirredsolution (500 rpm) of the polymeric dispersant the antifoaming agent andthe surfactant are added at ambient temperature (25° C.). The amounts ofthe materials are shown in Table 1 and are in percent by weight of thesolution.

Example 1.2

A reactor equipped with a stirrer and a heating mantle is filled with 26parts of polyphosphoric acid and heated to 90° C. Within 15 min 44.2parts of 2-phenoxyethanol are charged into the reactor. After 1 hour,400 parts of poly(ethyleneoxide)monophenylether (average molecularweight 5000 g/mol), 31.4 parts of concentrated methane sulfonic acid, 20parts of water and 12.6 parts of paraformaldehyde are added. Thisreaction mixture is stirred at 105° C. for 6 hours. After cooling, 550parts of water are added and the reaction mixture is neutralized with50% sodium hydroxide solution to a pH value of 6.5 to 7. The resin is alight brown colored, clear and aqueous polymer solution with a solidconcentration of 40% by weight. To the stirred solution (500 rpm) of thepolymeric dispersant the antifoaming agent and the surfactant are addedat ambient temperature (25° C.). The amounts of the materials shown inTable 1 are in percent by weight of the solution.

Example 1.3

A reactor equipped with a stirrer and a heating mantle is filled with51.6 parts of polyphosphoric acid and heated to 90° C. Within 15 min 90parts of 2-phenoxyethanol are charged into the reactor. After 1 hour,322 parts of poly(ethyleneoxide)monophenylether (average molecularweight 5000 g/mol), 300 parts of poly(ethyleneoxide)monophenylether(average molecular weight 2000 g/mol), 42.1 parts of concentratedmethane sulfonic acid, 16.8 parts of water and 28.5 parts ofparaformaldehyde are added. This reaction mixture is stirred at 105° C.for 6 hours. After cooling, 800 parts of water are added and thereaction mixture is neutralized with 50% sodium hydroxide solution to apH value of 6.5 to 7. The resin is a light brown colored, clear andaqueous polymer solution with a solid concentration of 40% by weight. Tothe stirred solution (500 rpm) of the polymeric dispersant theantifoaming agent and the surfactant are added at ambient temperature(25° C.). The amounts of the materials shown in Table 1 are in percentby weight of the solution.

Example 2 Formulation of Sample Additive Blends

Examples E1 to E20 were prepared by mixing the polycondensationcomponent (“polycondensate” of Table 1) with equivalent amounts (wt. %)of the dispersants according to Table 1. MELFLUX® PCE 239 L 45% N.D,MELFLUX® 2500 L 45% N.D., MELFLUX® 2453 L 44% N.D. MELFLUX® 2424 L 50%N.D., MELFLUX® AP 120 L 40%, and SOKALAN® DS5009 X are polycarboxylateether dispersants available from BASF Construction Polymers GmbH,Germany. MELCRETE® 500 L is a naphthalene sulfonate dispersant (BNS)available from BASF Construction Polymers GmbH, Tröstberg, Germany.MELMENT® L 15 G is a melamine sulfonate-formaldehyde condensate (MFS)available from BASF Construction Polymers GmbH. The non-ionic polymersN1 and N2 are able to maintain the fluidity of a cement composition andare synthesized according to the still unpublished application U.S. Ser.No. 12/477,637, herein incorporated by reference. Examples C7, C8 and C9are presented in Table 2 of Example 3.

TABLE 1 Formulation Molar Ratio (E: Invention; Polycondensate of poly-Solid C: according to condensate content Stability over Comparison)example Dispersant to dispersant (wt. %) 3 months E1 C7 Melflux PCE 2/135 stable 239 L E2 C8 Melflux PCE 2/1 35 stable 239 L E3 C7 BNS 1/1 25stable E4 C8 BNS 1/1 25 stable E5 C9 BNS 1/1 25 stable E6 C8 Melflux2500 L 1/1 40 stable E7-1 C8 Melflux PCE 3/1 40 stable 493 L E7-2 C8Melflux PCE 1/3 40 stable 493 L E8-1 C8 Melflux PCE 3/1 35 stable 239 LE8-2 C8 Melflux PCE 1/3 35 stable 239 L E9 C8 BNS 2/1 20 stable E10 C8Sokalan 2/1 35 stable 5009X E11 C8 Melflux AP 2/1 40 stable 120 L E12 C8Melment L 15 G 2/1 40 stable E13 C8 N1 2/1 30 stable E14 C8 Melflux PCE2/1 40 stable 493 L E15 C9 Melflux PCE 2/1 40 stable 493 L E16 C7 BNS3/1 25 stable E17 C7 Melflux 2500 L 1/1 40 stable E18 C7 Melflux 2453 L1/1 40 stable E19 C7 Melflux 2424 L 1/1 40 stable E20 C8 N2 2/1 30stable C1 — Melflux 2500 L 40 C2 — Melflux PCE 35 239 L C3 — Melflux PCE40 493 L C4 — 1:1 mixture 25 gel formation of Melflux 2500 L/BNS

Example 3 Formulations of Polycondensation Components withSurface-Active Properties and Antifoaming Agents

In the following admixtures, antifoaming agent A1 was apolypropyleneglycol commercially available as PLURIOL® P2000 and,antifoaming agent A2 an alkoxylated alcohol commercially available asDEGRESSAL® SD23 and antifoaming agent A3 a carboxylic ester commerciallyavailable as DEGRESSAL®SD30 all from BASF SE (Ludwigshafen, Germany).Surfactant S1 was an ethoxylated oxo-alcohol commercially available asLUTENSOL® 106 from BASF SE (Ludwigshafen, Germany). Surfactant S2 is astyrene/maleic acid comb-branched copolymer with polyether side chainswhich was synthesized according to EP 0306449 A2, herein incorporated byreference.

TABLE 2 Solution (E: Poly- Antifoaming Stability Invention; condensateagent Surfactant over 3 C: according to (wt.-%) (wt.-%) monthsComparison) example A1 A2 A3 S1 S2 at RT E21 E1 0.4 0.6 + E22 1.1 0.20.3 + E23 1.1 0.4 0.6 + E24 E2 0.2 0.3 + E25 1.2 0.2 0.3 + E26 1.2 0.40.8 + E27 1.2 0.2 0.3 + E28 1.1 0.2 0.3 + E29 1.3 0.2 0.3 + E30 E1 0.20.3 + E31 E2 0.2 0.3 + C5 1.1 0.4 −)* C6 1.2 0.4 −)* C7 1.1 None NoneNone None None n.a. C8 1.2 None None None None None n.a. C9 1.3 NoneNone None None None n.a. )* phase separation within two days

Example 4 Efficacy and Retardation of Additives in Gypsum

Combinations of dispersant components and polycondensation componentswere tested in the lab to determine dispersant efficacy and setretardation in a stucco slurry. Six hundred grams of stucco calcinedfrom a synthetic gypsum produced by flue gas desulfurization weremeasured for each test. Other components were added in amounts ofTable 1. CSA is a set accelerator as described above. The listed amountof water included a measured amount of gauging water plus water includedin any of the additives. Both the dispersant component and thepolycondensation component were diluted to 20% component solids byweight dispersed in water. The total dosage of the additive formulationblend shown in Table 3 was measured as weight of the component solidsbased on the weight of the dry stucco.

Composition of the test samples are shown in Table 3. One blendcomponent was MELFLUX® PCE 652 (hereinafter “PCE”), a commerciallyavailable polycarboxylate ether dispersant available from BASFConstruction Polymers, GmbH (Tröstberg, Germany). Melflux PCE 652 is apolycarboxylate ether dispersant combined with an antifoaming agent. Twodifferent blends of the polycondensation component with the surfactantof the S2 type and an antifoaming agent, labeled EPPR 395, and EPPR 568(BASF Construction Polymers, Tröstberg, Germany), were preparedaccording to Example 3. Samples EPPR 395 and EPPR 568 were made of thesame base polymer, however, EPPR 395 had four times the amount ofantifoaming agent as EPPR 568. Hereinafter, “EPPR” refers to blends ofthe polycondensation product, antifoaming agent and a comb-branchedcopolymer with polyether side chains.

Gauging water and the additive formulation blend were placed in the bowlof a HOBART® Brand mixer equipped with a mixing paddle and set on mixingspeed 2 for the entire procedure. The water and additive formulationblend were stirred thoroughly to ensure a complete mixing of theseingredients.

TABLE 3 Test Slurry Compositions Additive Formulation Blend EPPR PCE A-A- Water CSA EPPR mount, mount, Ratio, Dosage Run (g) (g) Type g gEPPR:PCE (%) 48 456 0.75 395 1.50 0 100:0 0.050 51 456 0.70 395 0.960.32 75:25 0.043 52 456 0.70 395 0.56 0.56 50:50 0.037 58 456 0.70 3950.22 0.67 25:75 0.030 60 456 0.75 — 0 0.83 0:100 0.028 6 420 0.85 3953.00 0 100:0 0.100 57 420 0.95 568 1.97 0.66 75:25 0.088 10 420 1.00 5681.20 1.20 50:50 0.080 15 420 1.10 568 0.52 1.57 25:75 0.070 20 420 1.20— 0 1.95 0:100 0.065 19 360 0.90 395 6.00 0 100:0 0.200 61 360 1.35 5684.28 1.42 75:25 0.190 26 360 1.65 568 2.40 2.40 50:50 0.160 31 360 2.10568 1.05 3.15 25:75 0.140 37 360 2.60 — 0 4.13 0:100 0.138 68 324 0.80568 9.00 0 100:0 0.300 35 324 0.80 395 9.00 0 100:0 0.300 70 324 1.90568 6.41 2.14 75:25 0.285 40 324 2.60 568 3.45 3.45 50:50 0.230 41 3243.50 568 1.50 4.50 25:75 0.200 46 324 7.50 — 0 6.45 0:100 0.215

A foam generator was used to pregenerate foam for addition to the slurryto produce a predetermined target wet density. Foam was generated at therate of 136 g/minute at an air flow of 2.0 L/min and foam density of0.065 g/cm³. The soap was supplied at the concentration shown in Table4. It was a mixture of 25AS (forms unstable foam) and PFM33 (formsstable foam) at the stated ratio for each run. The duration of the foamaddition, reported below as the “foam time” was determined by trial anderror to achieve a consistent target density.

The amount of CSA accelerator was adjusted at each dosage to give aninitial stiffening rate of 2 minutes. Stucco was preblended in a bagwith the CSA, then slowly and evenly added to the contents of the mixingbowl within 15 seconds. The stucco in the mixing bowl was allowed tosoak for 15 seconds. After raising the mixer bowl, the mixer was startedand mixed for 25 seconds. During mixing, foam was added to the slurryfor the duration listed in Table 4 as described below. Initiation offoam addition was timed so that the foam addition just completed at theend of the mixing period. The slurry was mixed for an additional 5seconds after foam addition was complete.

When mixing was completed, the mixer was stopped and a portion of theslurry was immediately poured into a damp 2 inch diameter by 4 inch tallcylinder placed on a plastic sheet, slightly overfilling the cylinder.Excess material was screeded from the top, then the cylinder was liftedup smoothly, allowing the slurry to flow out the bottom, forming apatty. The patty was measured (±1 mm) in two directions 90° apart, andthe average of the two measurements was reported as the patty diameter.A second sample of the slurry was poured into a cup of constant volumeand weighed to determine the cup weight. The wet density was calculatedfrom the weight of slurry in the cup and the known cup volume. Aftercomplete hydration, the sample of gypsum from the cup was broken open todetermine the size and distribution of internal voids.

TABLE 4 Foam Addition and Test Results Stiffening Soap Foam Run Slump(cm) Time Cup Wt. (g) (25AS:PFM33) Time(s) 48 17.8 2:05 228.75 0.5%(100:0) 10 51 17.8 2:10 219.01 0.5% (100:0) 11 52 18.3 2:10 224.96 0.5%(100:0) 10 58 18.0 2:10 224.49 0.5% (100:0) 10 60 17.7 2:10 225.57 0.5%(100:0) 10 6 18.1 2:10 218.60 0.5% (90:10) 11 57 17.8 2:10 216.49 0.5%(100:0) 11 10 18.2 2:15 213.82 0.5% (90:10) 11 15 18.0 2:10 218.24 0.5%(75:25) 11 20 17.8 2:10 218.97 0.5% (60:40) 11 19 18.3 2:10 201.70 0.5%(60:40) 14 61 18.0 2:15 202.82 0.5% (70:30) 14 26 18.0 2:15 200.45 0.5%(55:45) 14 31 17.8 2:15 204.28 0.5% (0:100) 14 37 17.8 2:20 201.91 0.7%(0:100) 13 68 18.0 2:10 195.81 0.5% (70:30) 15 35 17.9 2:10 192.03 0.7%(0:100) 15 70 17.9 2:05 197.01 0.5% (70:30) 15 40 17.7 2:10 195.10 0.7%(0:100) 14 41 18.1 2:15 194.03 0.7% (0:100) 14 46 17.7 2:35 200.35 0.8%(0:100) 13

Results from these tests are shown graphically in FIG. 4. The graphshows the amount of dispersant needed to produce a slurry of consistentviscosity (as shown by the slump test) and set time. Tests wereperformed with various blends at different number of water to stuccoratios.

Blends of EPPR 568 and PCE or EPPR 395 and PCE affect the efficacy ofthe combination in addition to the retardation. When looking at efficacyor retardation by itself, PCE has greater efficacy and both EPPR samplesminimize set retardation. At constant hydration time, using a blend ofEPPR 568 and PCE reduces set retardation and results in reduction in theamount of CSA accelerator that was required compared to slurries havingPCE alone. However, as seen in FIG. 5. at very low total dispersantdosage levels, around 0.05%, the change in accelerator amount betweenthe blends is minimal, implying that at low concentrations, differencesin set retardation between the two dispersants is minimal. Therefore,the use of PCE by itself or blends of EPPR 568/PCE with a higher PCEratio would be the most advantageous at low dosage levels to takeadvantage of the high efficacy of the PCE.

For moderate water reduction using higher total dispersant dosages(around 0.15% to 0.25%), a 1:1 blend of PCE:EPPR 568 is useful tobalance the amount of water reduction with the set accelerator usage.When trying to achieve even greater water reduction by using much highertotal dispersant dosages (greater than 0.25%), it would be moreadvantageous to use a high ratio of EPPR 568:PCE due to its reduced setretardation.

Blends with higher PCE amounts required more stable soap to produce asuitable void structure at a constant hydration time and fluidity.Conversely, as more EPPR 395 or EPPR 568 was used in the blend, moreunstable soap was needed to maintain the void Structure B. The trend wasevident in FIG. 6 at the 70 (420 g water), 60 (360 g water), and 54 (324g water) WSRs, especially noticeable at the 60 and 54 WSRs. At thelowest WSR tested, only the blend of 75% EPPR 568/25% PCE allowedreasonable control of the bubble structure at the original dosage.Blends with lesser amounts of EPPR 568 or EPPR 395 all required 100%stable soaps at higher concentrations. For example, at the 60 WSR, theEPPR 568/PCE 25/75 blend unstable ratio increased from 0% to about 60%for the EPPR 568/PCE 50/50 blend, which is a considerable change. Asimilar increase was observed at the 54 WSR with EPPR 568/PCE 50/50blend to the EPPR 568/PCE 75/25 blend from an unstable ratio of 0% to70% respectively.

This demonstrates the versatility of using the different blends in orderto be able to control core void size. Changes can be made in the blendmore towards PCE if larger void sizes are required and changed moretowards EPPR if smaller void sizes are required. This allows for evenmore precise control over the foam bubble size over a wide range ofoperating parameters. Some starches are known to destabilize the foam,increasing the complexity of the process. Increasing the ratio of EPPRto PCE stabilizes the foam without having to increase the amount ofstable soap. Better control over the bubble size is obtained withoutgoing to the extreme ends of the unstable:stable soap ratio or soapconcentrations.

As previously mentioned, when only EPPR 568 is being used to achievewater reduction, the extent of the water reduction can be limited by theadverse effects on foam void structure. At higher WSRs and constantdispersant usage, the dispersant with its antifoaming agent are lessconcentrated. Dilution of the antifoaming agent results, adverselyaffecting the foam. More defoamer is needed to achieve the correct foamvoid size. This can be accomplished by adding a PCE containing anantifoaming agent or a separate antifoaming agent. At the 76 WSR tested(456 g water) in this case, EPPR 395 and PCE dispersants both containinglarge amounts of antifoam agents were required in order to maintainbubble size at the 100% unstable soap ratio. (FIG. 6) However, as higherdispersant levels are used to lower the WSR, the concentration of thedispersant's defoamer component in the slurry also increases which canlead to excessively large bubble sizes. The increase in the amount ofdefoamer can come either by increasing the total dosage of the blendeddispersants or by increasing the ratio of the PCE to the EPPR atconstant total dosage. A higher ratio of EPPR to PCE is necessary toavoid excessively large bubble sizes.

Example 5 Blends Using Other Polycarboxylate Types

Additional tests using the materials, EPPR samples and test proceduresof Example 4 were performed using other commercially availabledispersants as the dispersant component blend. ETHACRYL® M Dispersant(CoAtex, LLC, Chester, S.C.) is a comb-branched polycarboxylatedispersant. MIGHTY 21 EG Dispersant is a polycarboxylate copolymer ofmethacrylic acid and is available from Kao Specialties Americas, LLC,(High Point, N.C.). Compositions of the test slurries are shown in Table5 and properties of the slurry and set materials are in Table 6.

Use of these additives also allows for better control of the core voidstructure. In the samples that follow, a slump size of 18 cm, stiffeningtime of 2 minutes 15 seconds and void Structure B were targetproperties. The use of the additive combinations made it easier toaddress the problems of efficacy, retardation and core structuresimultaneously.

TABLE 5 Test Slurry Compositions Additive Formulation Blend EPPR PCERatio, Dosage Run Water (g) CSA (g) Amount, g PCE Type Amount, gEPPR:PCE (%) 76 360 0.95 0 Ethacryl M 6.00  0:100 0.200 93 360 0.80 3.83Ethacryl M 1.27 75:25 0.170 79 360 0.95 2.40 Ethacryl M 2.40 50:50 0.16078 360 1.00 1.28 Ethacryl M 3.82 25:75 0.170 82 324 2.10 0 Ethacryl M11.10  0:100 0.370 97 324 0.70 4.95 Ethacryl M 1.65 75:25 0.220 95 3240.75 3.15 Ethacryl M 3.15 50:50 0.210 87 324 1.15 1.72 Ethacryl M 5.1825:75 0.230 111 360 0.85 0 Mighty 21G 0  0:100 0.270 115 360 0.80 2.25Mighty 21G 2.55 50:50 0.170

TABLE 6 Foam Addition and Test Results Stiff- Slump ening Cup Wt. SoapFoam Void Run (cm) Time (g) (25AS:PFM33) Time(s) Structure 76 17.9 2:20205.64 0.5% (100:0) 14 A 93 18.1 2:15 202.83 0.5% (75:25) 13 B 79 17.92:10 203.91 0.5% (100:0) 14 B 78 18.6 2:10 203.78 0.5% (100:0) 14 A 8218.0 2:20 200.88 0.5% (100:0) 15 A 97 18.1 2:10 199.80 0.5% (50:50) 15 B95 17.8 2:10 194.32 0.5% (75:25) 15 B 87 18.1 2:10 193.86 0.5% (100:0)18 B 111 17.8 2:20 197.28 0.5% (100:0) 13 A 115 18.0 2:20 202.63 0.5%(80:20) 14 B

Surprisingly, combination of the polycondensation component with theEthacryl M and Mighty 21G brand dispersant components gave differentresults than when used with Melflux brand dispersants. The combinationsof Example 4 demonstrated a change in efficacy but little change inbubble size in the set samples. However, in this example with differentpolycarboxylate dispersants, efficacy varied less but increased controlover void structure was observed.

Example 6

A polycondensate product component (EPPR) was prepared according toExample 3 and surfactant S2, also from Example 3, was used as thedispersant component. The set retarder was Versenex 80, which is apentasodium diethylenetriaminepentaacetate set retarder (Dow Chemical,Midland, Mich.) and is used as a 20% solution. Other materials and testconditions of Example 4 were repeated with various combinations of theseadditives as noted in Table 7 below:

TABLE 7 Test Slurry Compositions Additive Formulation Blend Water EPPRPCE PCE Ratio, Dosage Run (g) CSA (g) Amount, g Type Amt, g EPPR:PCE (%)Retarder, g 119 360 1.90 2.40 652 2.40 50:50 0.160 0 122 360 1.90 2.40652 2.40 50:50 0.160 0.25 125 360 0.90 5.70 None 0 100:0  0.190 0 127360 0.90 5.70 None 0 100:0  0.190 0.25

TABLE 8 Foam Addition and Test Results Stiffening Soap Foam Run Slump(cm) Time Cup Wt. (g) (25AS:PFM33) Time(s) 119 18.0 2:15 200.9 0.5%(50:50) 14 122 19.1 2:15 206.36 0.5% (50:50) 13 125 17.9 2:15 203.560.5% (60:40) 14 127 18.8 2:15 205.38 0.5% (60:40) 14

Slump increased from 17.9 cm to 18.8 cm while maintaining the samestiffening time by varying the amount of CSA set accelerator. Theseresults indicate that the addition of a small amount of retarder incombination with the dispersant component and polycondensation componentled to enhanced efficacy. This can be translated into additional waterreduction or lower dispersant usage.

Example 7

The effect of modifiers with the combined dispersant component andpolycondensation component was tested in a gypsum slurry. The gypsumslurry included stucco, 60 grams of water per 100 grams of stucco.Dispersants and polycondensation components were added until a pattysize of 17.8 cm+/−0.3 cm was obtained in a slump test. EPPR 568 was usedas the polycondensation component, while PCE 652 was the dispersantcomponent. Two sets of data were obtained, one using thepolycondensation component alone and the other using a 1:1 ratio byweight of the polycondensation component to dispersant component(“EPPR+PCE”). In each set of data, a control sample with no modifier wastested, together with samples with modifiers shown in Table 9 below.

TABLE 9 Sample Dispersant Dose Modifier 1 EPPR 0.22% None 2 EPPR 0.22%Lime 3 EPPR 0.20% Soda Ash 4 EPPR + 0.17% None PCE 5 EPPR + 0.14% LimePCE 6 EPPR + 0.13% Soda PCE Ash

Looking to the dispersant component and polycondensate componentcombination, an increase in efficacy was observed with both soda ash andwith lime. Use of the EPPR dispersant alone resulted in a reduction ofdosage with soda ash only. Although both dispersants demonstrated themodifying effect with soda ash, the EPPR:PCE blend showed a greaterdegree of improvement compared to the EPPR alone. The blend also allowedreduction in the dispersant dosage in the presence of lime.

Example 8

The samples of Example 7 were tested to determine the hydration effectsof the modifiers. The amount of dispersant component and polycondensatecomponent used was the same as in Table 9, while the amount of CSA setaccelerator was changed as necessary to obtain information as to the setretardation of the mixtures. The amount of CSA set accelerator wasvaried according to Table 10 to produce a slurry with a stiffening pointof 2:10+/−0:05.

TABLE 10 Amt. Sample Dispersant Modifier Dose CSA 1 EPPR None 0 1.1 g 2EPPR Lime 0.15% 0.9 g 3 EPPR Soda 0.04% 4.5 g Ash 4 EPPR + None 0 2.8 gPCE 5 EPPR + Lime 0.15% 2.7 g PCE 6 EPPR + Soda 0.04% 6.5 g PCE Ash

It is clear from the data above that soda ash can retard the hydrationreaction of calcined gypsum significantly, while lime has a slightaccelerating effect in this example. The 1:1 blend of EPPR and PCEdemonstrated a more pronounced retardation in the control sample as wellas when modifiers were added compared to using EPPR alone.

Example 9 Comparative Example of Method

Attempts were made to prepare a gypsum slurry having a slump size of17.8 cm+/−0.3 cm, a stiffening time of 2:10+/−0:05 and a mixed corebubble size distribution. This example demonstrates the steps that mustbe taken when the present method is not utilized.

Step A: A slurry was prepared according to Example 4 that included 600 gof synthetic gypsum, a WSR of 60 and 1.8 g CSA accelerator. A blend of25% EPPR 568 and 75% PCE 652 was added to the slurry at a dosage of0.13% of total dispersants solids by weight of the dry calcined gypsum.Foam was generated using a 1:1 blend of 25AS and PFM33 at a dosage of0.5% based on total soap solution. Testing of the slurry revealed thatthe slump was 18.7 cm, the stiffening time was 2:40 and the bubbles weretoo large.

Step B: In order to reduce the bubble size distribution in the productof Step A, the amount of stable soap was increased from 50% of the soapblend to 100% of the soap. All other components and preparation stepsremained the same. This second product had a smaller slump at 18.3 cmand smaller bubbles. The stiffening time remained the long at 2:40.

Step C: To reduce the stiffening time in the product of Step B, theamount of CSA set accelerator was increased from 1.8 g to 2.1 g. Thestiffening time was reduced to 2:30, but was still too long. The bubblesize was slightly smaller, bring it into the desired range, but thestiffening was still too long.

Step D: The amount of CSA set accelerator was increased in the Productof Step C from 2.1 g to 2.8 g to bring the stiffening into range. Bubblesize and stiffening time were within range, but the resulting slump sizewas now too small.

Step E: To increase the slump size, the amount of dispersant in theproduct of Step D was increased from 0.13% to 0.14% based on the weightof dry calcined gypsum to improve the flowability of the slurry. Thisresulted in bringing the bubble size, the stiffening time and the slumpinto the appropriate range. These steps can be performed in any order toobtain the final desired parameters.

Example 10

Instead of changing the soap composition, the amount of set acceleratorand the dosage of dispersant, the product of Step A was changed bychanging the ratio of EPPR to PCE from 25:75 to 40:60. This singlechange resulted in a stiffening time of 2:20, a slump size of 17.5 cmand a good bubble size distribution. Adapting the ratio of thepolycondensation component to the dispersant component not only resultedin a more direct method of obtaining the desired properties, but itresulted in smaller amounts of additives being utilized, saving time,money and raw materials. This provides for another tool to be utilizedwhen changes in other methods are insufficient.

While particular embodiments of the gypsum panels have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges and modifications may be made thereto. Unless otherwise noted,features of specific embodiments may be combined with any other featuresdescribed. Unless otherwise noted, all ratios or percentages expressedherein are intended to be based on weight. The term “or” is intended tobe inclusive of combinations of elements in a given list. These andother modifications may be made without departing from the invention inits broader aspects and as set forth in the following claims.

What is claimed is:
 1. A gypsum slurry comprising: calcium sulfatehemihydrate; water; a dispersant component selected from the groupconsisting of a comb-branched polymer having polyether side chains,naphthalene sulfonate-formaldehyde condensate, melaminesulfonate-formaldehyde condensate and mixtures of two or more thereof; afoaming agent; and a polycondensation component comprising: a firstpolycondensation repeating unit having a polyether side chain and one ofthe group consisting of an aromatic sub-unit and a heteroaromaticsub-unit; a second polycondensation repeating unit having a OP(OH)₂group and one of the group consisting of an aromatic sub-unit and aheteroaromatic sub-unit; and a third polycondensation repeating unithaving one of the group consisting of an aromatic sub-unit and aheteroaromatic sub-unit; wherein said second polycondensation repeatingunit and said third polycondensation repeating unit differ exclusivelyin that the OP(OH)₂ groups of said second polycondensation repeatingunit are replaced by H in said third polycondensation repeating unit,and said third polycondensation repeating unit is not the same as saidfirst polycondensation repeating unit; and wherein the weight ratio ofthe dispersant component to the polycondensation component ranges from1:99 to 75:25.
 2. The gypsum slurry of claim 1 wherein one of the groupconsisting of said dispersant component, said polycondensation componentor both further comprises an antifoaming component.
 3. The gypsum slurryof claim 1 wherein said dispersant component is said comb-branchedcopolymer having polyether side chains and comprises: at least one firstpolycarboxylate repeating unit derived from an olefinically unsaturatedmonocarboxylic acid comonomer or an ester or a salt thereof and anolefinically unsaturated sulfonic acid comonomer or a salt thereof; andat least one second polycarboxylate repeating unit of the generalformula (I)

wherein R¹ is

and R² is H or an aliphatic hydrocarbon radical having 1 to 5 C atoms;R³ is an unsubstituted or substituted aryl radical and R⁴ is H, analiphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatichydrocarbon radical having 5 to 8 C atoms, a substituted aryl radicalhaving 6 to 14 C atoms, or one of the group consisting of:

wherein R⁵ and R⁷ each represent an alkyl, aryl, aralkyl or alkarylradical; R⁶ represents an alkylidene, arylidene, aralkylidene oralkarylidene radical; p=0, 1, 2, 3 or 4; m and n each, independently ofone another, is 2, 3, 4 or 5; x and y each, independently of oneanother, is an integer≦350; and z is from 0 to about 200; and whereineither the first and second polycarboxylate repeating units have nointernal molecular differences or said first and second polycarboxylaterepeating units have internal molecular differences with respect to atleast one of said radicals R¹; R²; R³; R⁴; R⁵; R⁶; R⁷; m; n; x; y; andz, and the differences relate to the composition and length of sidechains.
 4. The gypsum slurry of claim 3, wherein said firstpolycarboxylate repeating unit is present in amounts of 30 to 99 mol %and said second polycarboxylate repeating unit is present in amounts ofabout 70 to about 1 mol % of the dispersant component.
 5. The gypsumslurry of claim 1, wherein said first polycondensation repeating unit ofthe polycondensation component is represented by Formula VII:

wherein A has 5 to 10 C atoms and is a substituted or unsubstitutedaromatic or heteroaromatic compound; B is N, NH or O; n is 2 if B is Nand n is 1 if B is NH or O; R¹ and R² each, independently of oneanother, is a branched or straight-chain C₁- to C₁₀-alkyl radical, C₅-to C₈-cycloalkyl radical, aryl radical, heteroaryl radical or H; a is aninteger from about 1 to about 300, X is a branched or straight-chain C₁-to C₁₀-alkyl radical, C₅- to C₈-cycloalkyl radical, aryl radical,heteroaryl radical or H; wherein said second polycondensate repeatingunit of said polycondensation component is represented by Formula(VIII):

wherein said third polycondensate repeating unit of saidpolycondensation component is represented by Formula (IX):

wherein in Formula (VIII) and Formula (IX) D is a substituted orunsubstituted heteroaromatic compound having 5 to 10 C atoms; E is N, NHor O; m is 2 if E is N and m is 1 if E is NH or O; R³ and R⁴ each,independently of one another, is a branched or straight-chain C₁- toC₁₀-alkyl radical, C₅- to C₈-cycloalkyl radical, aryl radical,heteroaryl radical or H; b is an integer from 0 to 300; M is an alkalinemetal ion, alkaline earth metal ion, ammonium ion, organic ammonium ionand/or H, and c is ½ if M is an alkaline earth metal ion, or else c is1; and wherein A, B, R¹, R², a, X, D, E, R³, R⁴, b, and M are each,independently of one another, identical or different among saidindividual first polycondensate repeating units.
 6. The gypsum slurry ofclaim 1 further comprising an additive selected from the groupconsisting of a set accelerator, a set retarder, an anti-sagging agent,a bonding agent, a dedusting agent, a reinforcing material, a biocideand combinations thereof.
 7. The gypsum slurry of claim 1 wherein saidfoaming agent is a mixture of a first foaming agent which forms stablefoam and a second foaming agent which forms unstable foam.
 8. A methodof making the gypsum slurry of claim 1 comprising: combining and mixingcalcium sulfate hemihydrate, water, the foaming agent, the dispersantcomponent and the polycondensation component to form the gypsum slurrywith foam bubbles, wherein the ratio of the dispersant component to thepolycondensation component is adjusted to control the size of the foambubbles.
 9. The method of claim 8 wherein the foaming agent is in theform of foam.
 10. The method of claim 8 further comprising adding anadditive selected from the group consisting of a set accelerator, a setretarder, an anti-sagging agent, a bonding agent, a dedusting agent, areinforcing material, a biocide and combinations thereof.
 11. A gypsumslurry comprising: calcium sulfate hemihydrate; water; a foaming agent;a comb-branched polymer having polyether side chains; and apolycondensation component comprising: a first polycondensationrepeating unit having a polyether side chain and one of the groupconsisting of an aromatic sub-unit and a heteroaromatic sub-unit; asecond polycondensation repeating unit having a OP(OH)₂ group and one ofthe group consisting of an aromatic sub-unit and a heteroaromaticsub-unit; and a third polycondensation repeating unit having one of thegroup consisting of an aromatic sub-unit and a heteroaromatic sub-unit;wherein said second polycondensation repeating unit and said thirdpolycondensation repeating unit differ exclusively in that the OP(OH)₂groups of said second polycondensation repeating unit are replaced by Hin said third polycondensation repeating unit, and said thirdpolycondensation repeating unit is not the same as said firstpolycondensation repeating unit; and wherein the weight ratio of thecomb-branched polymer having polyether side chains to thepolycondensation component ranges from 1:99 to 75:25.
 12. The gypsumslurry of claim 1, wherein said dispersant component is naphthalenesulfonate-formaldehyde condensate, melamine sulfonate-formaldehydecondensate or mixtures thereof.
 13. A gypsum product prepared from thegypsum slurry of claim 1 by allowing calcium sulfate hemihydrate tohydrate and form a calcium sulfate dihydrate matrix.
 14. The gypsumproduct of claim 13, wherein the product comprises voids of apredetermined size.
 15. A method of making a gypsum product, the methodcomprising preparing a gypsum slurry according to the method of claim 8,forming the gypsum product without depositing the gypsum slurry onto aconveyor and allowing calcium sulfate hemihydrate to hydrate and form acalcium sulfate dihydrate matrix.